Portsmouth (England)
The scariest ride I've ever been on was the little rollercoaster on the seafront at Portsmouth & Southsea.
As a ride it's nothing to worry about at all. It goes up, round and round, over a few bumps and that's it. The fact I know about the interactions of steel and seawater, rust, corrosion, metal fatigue and vibration scared the life out of me as we went round. I could see the state of the bolts holding it all together...
I survived the ride but wouldn't go on that one ever agian! In the end there never was an accident with it although it was scrapped a few months later!
Jason